Nitric oxide (NO) has been implicated as part of a cascade of interacting agents involved in a wide variety of bioregulatory processes, including the physiological control of blood pressure, macrophage-induced cytostasis and cytotoxicity, and neurotransmission (Moncada et al., “Nitric Oxide from L-Arginine: A Bioregulatory System,” Excerpta Medica, International Congress Series 897, Elsevier Science Publishers B.II.: Amsterdam (1990); Marletta et al., Biofactors 2: 219-225 (1990); Ignarro, Hypertension (Dallas) 16: 477-483 (1990); Kerwin et al., J. Med. Chem. 38: 4343-4362 (1995); and Anggard, Lancet 343: 1199-1206 (1994)). Given that NO plays a role in such a wide variety of bioregulatory processes, great effort has been expended to develop compounds and devices thereof capable of releasing NO to treat biological disorders such as restenosis. Some of these compounds are capable of releasing NO spontaneously, e.g., by hydrolysis in aqueous media, whereas others are capable of releasing NO upon being metabolized (Lefer et al., Drugs Future 19: 665-672 (1994)).
Methods to regulate endogenous NO release have primarily focused on activation of enzymatic pathways with excess NO metabolic precursors like L-arginine and/or increasing the local expression of nitric oxide synthase (NOS) using gene therapy. U.S. Pat. Nos. 5,945,452, 5,891,459, and 5,428,070 describe the sustained NO elevation using orally administrated L-arginine and/or L-lysine while U.S. Pat. Nos. 5,268,465, 5,468,630, and 5,658,565 describe various gene therapy approaches. Other various gene therapy approaches have been described in the literature. See, e.g., Smith et al., “Gene Therapy for Restenosis,” Curr. Cardiol. Rep., 2(1): 13-23 (2000); Alexander et al., “Gene Transfer of Endothelial Nitric Oxide Synthase but not Cu/Zn Superoxide Dismutase restores Nitric Oxide Availability in the SHRSP,” Cardiovasc. Res., 47(3): 609-617 (2000); Channon et al., “Nitric Oxide Synthase in Atherosclerosis and Vascular Injury: Insights from Experimental Gene Therapy,” Arterioscler. Thromb. Vasc. Biol., 20(8): 1873-1881 (2000); Tanner et al., “Nitric Oxide Modulates Expression of Cell Cycle Regulatory Proteins: A Cytostatic Strategy for Inhibition of Human Vascular Smooth Muscle Cell Proliferation,” Circulation, 101(16): 1982-1989 (2000); Kibbe et al., “Nitric Oxide Synthase Gene Therapy in Vascular Pathology,” Semin. Perinatol., 24(1): 51-54 (2000); Kibbe et al., “Inducible Nitric Oxide Synthase and Vascular Injury,” Cardiovasc. Res., 43(3): 650-657 (1999); Kibbe et al., “Nitric Oxide Synthase Gene Transfer to the Vessel Wall,” Curr. Opin. Nephrol. Hypertens., 8(1): 75-81 (1999); Vassalli et al., “Gene Therapy for Arterial Thrombosis,” Cardiovasc. Res., 35(3): 459-469 (1997); and Yla-Herttuala, “Vascular Gene Transfer,” Curr. Opin. Lipidol., 8(2): 72-76 (1997). In the case of preventing restenosis, however, these methods have not proved clinically effective. Similarly, regulating endogenously expressed NO using gene therapy techniques such as NOS vectors remains highly experimental. Also, there remain significant technical hurdles and safety concerns that must be overcome before site-specific NOS gene delivery will become a viable treatment modality.
The exogenous administration of gaseous nitric oxide is not feasible due to the highly toxic, short-lived, and relatively insoluble nature of NO in physiological buffers. As a result, the clinical use of gaseous NO is largely restricted to the treatment of neonates with conditions such as persistent pulmonary hypertension (Weinberger et al., “The Toxicology of Inhaled Nitric Oxide,” Toxicol. Sci., 59(1): 5-16 (2001); Kinsella et al., “Inhaled Nitric Oxide: Current and Future Uses in Neonates,” Semin. Perinatol., 24(6): 387-395 (2000); and Markewitz et al., “Inhaled Nitric Oxide in Adults with the Acute Respiratory Distress Syndrome,” Respir. Med., 94(11): 1023-1028 (2000)). Alternatively, however, the systemic delivery of exogenous NO with such prodrugs as nitroglycerin has long enjoyed widespread use in the medical management of angina pectoris or the “chest pain” associated with atherosclerotically narrowed coronary arteries. There are problems with the use of agents such as nitroglycerin. Because nitroglycerin requires a variety of enzymes and cofactors in order to release NO, repeated use of this agent over short intervals produces a diminishing therapeutic benefit. This phenomenon is called drug tolerance and results from the near or complete depletion of the enzymes/cofactors needed in the blood to efficiently convert nitroglycerin to a NO-releasing species. By contrast, if too much nitroglycerin is initially given to the patient, it can have devastating side effects including severe hypotension and free radical cell damage. Likewise, the use of nitrocellulose, a polymer analog of nitroglycerin, possesses potentially similar hazards as a source of NO, for example, as described in U.S. Published Patent Application 2004/0033242 A1, published Feb. 19, 2004.
One potential method for overcoming the disadvantages associated with NO prodrug administration is to provide NO-releasing therapeutics that do not require activation by endogenous enzyme systems. Early efforts to provide NO-releasing compounds suitable for in vivo use were described in U.S. Pat. No. 4,954,526.
Diazeniumdiolates comprise a diverse class of NO-releasing compounds/materials that are known to exhibit sufficient stability to be useful as therapeutics. Although discovered more than 100 years ago by Traube et al. (Liebigs Ann. Chem., 300: 81-128 (1898)), the chemistry and properties of diazeniumdiolates have been extensively reinvestigated by Keefer and co-workers, as described in U.S. Pat. Nos. 6,750,254, 6,703,046, 6,673,338, 6,610,660, 6,511,991, 6,379,660, 6,290,981, 6,270,779, 6,232,336, 6,200,558, 6,110,453, 5,910,316, 5,814,666, 5,814,565, 5,731,305, 5,721,365, 5,718,892, 5,714,511, 5,700,830, 5,691,423, 5,683,668, 5,676,963, 5,650,447, 5,632,981, 5,525,357, 5,405,919, 5,389,675, 5,366,997, 5,250,550, 5,212,204, 5,208,233, 5,185,376, 5,155,137, 5,039,705, and 4,954,526, and in Hrabie et al., J. Org. Chem., 58: 1472-1476 (1993), which are incorporated herein by reference.
Diazeniumdiolated compounds have been attached to polymers, substrates, and medical devices. See, for example, U.S. Pat. Nos. 6,703,046, 6,270,779, 6,673,338, 6,200,558, 6,110,453, 5,718,892, 5,691,423, 5,676,963, 5,650,447, 5,632,981, 5,525,357, and 5,405,919.
Keefer et al. (U.S. Pat. Nos. 4,954,526; 5,039,705; 5,155,137; 5,208,233, 5,525,357, 5,405,919, 5,718,892, 5,676,963, and 6,110,453 and related patents and patent applications, all of which are incorporated herein by reference) and Smith et al. (U.S. Pat. No. 5,691,423 which is incorporated herein by reference) disclose, among others, the use of certain nucleophile/nitric oxide adducts as NO-releasing agents, i.e.,
in which the nucleophile residue (Nuc) preferably is a primary amine, a secondary amine, or a polyamine. Although such adducts offer many advantages over other currently available nitric oxide-releasing compounds, one disadvantage presented by the use of such adducts as pharmaceutical agents is the potential risk of release of nitrosamines, which are carcinogenic, upon decomposition and release of NO. Another disadvantage of the adducts of primary amines is that they can be unstable even as solids due to a tendency to form traces of potentially explosive diazotates.
Furthermore, several types of compounds of the general structure
are known. See Hrabie and Keefer, Chem. Rev. 102, 1135-1154 (2002) for a review of diazeniumdiolate chemistry. Traube (Liebigs Ann. Chem. 300: 81-123 (1898)) reported the preparation of a number of such compounds and noted that treatment of the compounds with acid produced a “brown gas.” Although brown gas suggests the release of NO, given that a brown gas also may be produced in the disproportionation of nitrite, the release of brown gas by the compounds prepared by Traube is not, in and of itself, evidence of NO release. Compounds of the structural type reported by Traube were believed to require harsh treatment with mineral acids to release any gas.
The prior art teaches that an [N2O2−] functional group bonded to a carbon atom through the above-described Traube reaction releases NO only after harsh treatment with mineral acids, making such compounds incompatible with biological utility. Further, Smith et al. (U.S. Pat. No. 5,691,423), for example, teaches the use of a nucleophile adduct in a two-step process to link a nitrogen-bound [N2O2−] functional group to a carbon atom of a polysaccharide in order to obtain NO release. However, the compounds described in Smith et al. have the potential risks of releasing carcinogens upon decomposition and release of NO, and being relatively unstable. Finally, the prior art teaches another two-step process to link a nitrogen-bound [N2O2−] functional group to a carbon atom of a polysaccharide. See Kugelman et al., J. Chem. Soc. Perkin I, 1113-1126 (1976). However, the method of Kugelman et al. results in the polysaccharide further comprising a reactive halogen atom.
Thus, despite the extensive literature available on NO and nitric oxide-releasing compounds, there remains a need for stable nitric oxide-releasing polymers, such as polysaccharides, or small molecules, such as monosaccharides and disaccharides, that exhibit a sustained release of nitric oxide and can be readily prepared during the processing of commercially available material containing monosaccharides, disaccharides, polysaccharides, or any combination thereof. Moreover, there exists a need for medicines and medical devices capable of releasing NO for an efficacious duration. Such a medicine or device is useful for treating biological disorders.